article: If someone asks you to draw a picture of a robot, what will it look like? Like a person? We always think the robot looks like a person. But real robot have many different looks. What robots look like has something to do with the jobs they do.
  Robot don't get bored. They don't get tired. They don't worry about getting dirty.
  Some people are worried that robots will become the _ of the earth one day. But I think it won't happen. After all, robots are controlled   by people. They work according to people's orders.
  With the help of robots, we are living a safer, happier and more comfortable life.
question: According to the passage, why won't robot become the ruler of the earth?
options: Because they move quickly. Because they are controlled by people. Because they help people a lot. Because they need to sleep.